[Octave-bug-tracker] [bug #32700] nargout(fn) Matlab compatibility

[anonymous]

URL:
  <http://savannah.gnu.org/bugs/?32700>

                 Summary: nargout(fn) Matlab compatibility
                 Project: GNU Octave
            Submitted by: None
            Submitted on: Mon 07 Mar 2011 11:35:27 UTC
                Category: Interpreter
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Feature Request
                  Status: None
             Assigned to: None
         Originator Name: Iain Murray
        Originator Email: address@hidden
             Open/Closed: Open
         Discussion Lock: Any
                 Release: dev
        Operating System: GNU/Linux

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Details:

In Matlab the nargout function can take a function handle or name and will
return the number of output arguments that it takes. The number is negative
for variable numbers of outputs and (undocumented) -1 if the number is
variable "[varargout]".

In Octave (according to the documentation) "At the top level, `nargout' is
undefined." The only functions Octave will report nargout for are those within
the same m-file (and Octave 3.2.3 reports -1 for those regardless). Support
for function handles has not been implemented at all. Example output in Matlab
and Octave are given below.

Use case: I ran into this compatibility wishlist item while trying to use a
routine for robustly timing functions:
    http://www.mathworks.com/matlabcentral/fileexchange/18798
    (Motivated here:
http://blogs.mathworks.com/steve/2008/02/29/timing-code-in-matlab/ )
This routine works in Octave if its second input argument is specified, as
then nargout isn't called. Otherwise it crashes.

----


>> fn = @() deal(1,2,3)
fn = 
    @()deal(1,2,3)
>> nargout(fn)
ans =
    -1


----


octave:1> fn = @() deal(1,2,3)
fn =

@() deal (1, 2, 3)

octave:2> nargout(fn)
error: octave_base_value::convert_to_str_internal (): wrong type argument
`function handle'
error: nargout: expecting string as first argument


----


% Set foo.m to contain the following:
function foo()
nargout('bar')
function [a,b,c] = bar()
[a,b,c] = deal(1,2,3);


Running foo in Matlab prints out '3', whereas Octave prints out '-1'.

----

I'm not familiary enough with Octave internals to immediately write a patch. I
just got as far as finding nargout implemented at the line beginning "DEFUN
(nargout," in ov-usr-fcn.cc




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